Feed fractionation of a silica sand sample to a rare earth roll separator (RER) magnetic separator was found to be much more favorable for separation than the whole batch. The performance of the separator depends on both the size and the size distribution of the feed. The correlation between the different size fractions of the feed, e.g., -0.6+0.106, -0.6+0.211, and -0.211+0.106mm and the RER magnetic parameters, e.g., belt speed and splitter angle of inclination was statistically verified using the central composite design (CCD) to achieve the optimum performance of the separator to reduce the Fe2O3 content of the sand concentrate. About 56.6% removal of this contaminant was achieved with the whole feed -0.6+0.106mm at belt speed of 100rpm and splitter angle inclination of 95 degrees, whereas 84.3% reduction of Fe2O3 content was achieved with the separate size fractions under different belt speed and splitting angle inclination optima. The quality of the silica sand concentrate produced satisfies the requirement for both colorless glass and insulating glass fibers production.